Diesel engines of the type used in motor vehicles are subject to increasingly stringent emissions requirements. As a result, fuel injector nozzles used in diesel engines must be manufactured to rather strict fuel flow tolerances, for example, flow tolerances of .+-.0.3 pounds per hour (PPH) total error band. The nozzles must be tested individually prior to installation in an engine to determine whether the fuel flow performance falls within the required tolerances for emission control purposes. Typically, the fuel injector nozzles will be classified as "accepts" or "rejects" depending upon the flow test results; i.e. "accepts" will have satisfied the required flow tolerances whereas "rejects" will have fallen outside the required flow tolerances.
In order to flow test diesel engine fuel injector nozzles for emission control purposes, flow test systems of improved accuracy are needed to provide the extremely narrow flow error bands that will distinguish "accepts" from "rejects." To this end, the flow test systems require a flow generating apparatus that can provide a precise flow of fluid (actual or simulated fuel) as a primary flow standard for supply to each fuel injector nozzle tested. A flow generating apparatus of this type that does not require periodic active calibration and is capable of self-pumping to eliminate the need for a high pressure fluid pump would be highly desirable in an engine assembly facility for testing large numbers of fuel injector nozzles prior to installation in the engines.
An object of the present invention is to provide a precision fluid flow generating apparatus which satisfies these needs and thus is especially useful for, although not limited to, use in the flow testing of fuel injector nozzles.